What causes the valve stem to rotate?
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This post was last edited by zyzs on 2011-4-15 05:29. It involves Chuanyi control valves, sleeve valves, reaction-type air-operated valves, with high-pressure steam as the medium. There is significant vibration; the valve stem moves upward (not by much) and also rotates, to the point that the feedback rod vibrates violently. It’s possible that the pressure difference before and after the valve is too large, or there was an error in the valve selection. I would like to ask what causes the valve stem to rotate – could it be due to the screws used to secure the valve stem inside the diaphragm head?
Reply to 1# zyzs: Was a single-seat valve, a sleeve valve, or some other type of valve chosen for the valve? Is it an open airway or a closed airway? What is the valve opening degree? When asking a question, be sure to make it clear
There are several reasons for the valve stem to move up and down back and forth: (1) The input signal to the actuator is interfered with or inaccurate, causing the actuator to command the valve to move up and down. (2) The pressure difference across the control valve is too large, resulting in a significant unbalanced force acting on the valve stem. The thrust generated by the actuator is not sufficient to overcome this unbalanced force, causing the valve stem to move up and down ； Furthermore, an excessive pressure difference leads to a high steam flow rate, which in turn causes the valve core to rotate along with the high-speed steam. To address these issues, first, use multi-stage pressure-reducing control valves with a slightly larger diameter. A larger diameter helps to reduce the flow velocity at the inlet and outlet of the valve. Through the multiple small holes in the pressure-reducing sleeves, the steam pressure and flow velocity are reduced step by step, which effectively reduces the impact of high-speed fluid on the valve core, thereby minimizing the rotational forces and imbalances acting on it. Additionally, using a more powerful actuator provides further safety.
There is a large cover on top of the diaphragm head; once it is opened, there should be a screw used to secure the rotation of the valve, and a socket wrench is required to remove it. After adjusting the valve stem, the locator needs to be reset to its original position. As for the reasons, everyone upstairs has explained them clearly, so I won’t repeat them. It’s also possible that a leak in the gas supply pipe could cause the valve stem to vibrate.
The selection estimate is likely correct; it’s a problem on-site.
At what opening degree does vibration occur? I think choosing the wrong valve diameter can cause vibration in the valve, or disturbances in its positioning on site can lead to up-and-down movement, while an unstable air supply can also cause such movement.
Are it newly purchased valves being used, or are they old ones? 1. If it’s old valves that are causing such problems, then it’s definitely not a matter of improper selection. There are many factors that can cause issues with the valve stem’s movement; I think it’s necessary to first check whether there are any problems with the manufacturing process, such as fluctuations in that process. It’s important to communicate more closely with those responsible for the manufacturing process – we shouldn’t assume that the problem always lies with the valves (this mindset needs to change). Only if there are indeed no issues with the manufacturing process should we then examine the control valve, checking whether the bolts securing the diaphragm are loose, as well as whether the connections at the valve stem are loose. If nothing else seems to be wrong, then the valve needs to be disassembled to determine whether the valve element has been damaged due to years of use. An appropriate maintenance plan should then be developed for repairs. 2. If it’s a new valve, the key lies in the selection process; once the selection is correct, then other aspects can be checked! I’m not sure if these will help you!
I have also used this type of valve for regulating high-pressure steam, and the phenomenon is the same. The main reason is that the pressure difference before and after is too large, causing the valve to be subjected to unbalanced forces. This is the case when the opening degree used is often at the critical force level. After installing a manual valve in series, the situation was alleviated as the pressure difference was reduced.
This one should be chosen with a balance hole; if it’s changed, this kind of problem shouldn’t occur! Is it also because the valve stem isn’t properly fixed?
Increasing the spring stiffness raises the actuator output pressure.
It’s likely a matter of selection; nowadays, many design firms choose long-necked types for high-pressure steam control valves, which results in a reduced stiffness of the valve stem and increased susceptibility to vibration. It would be better to use those with improved heat dissipation capabilities